The recent research data have revealed that, besides their immune systems, almost all living organisms have an additional defense system against invasion of pathogenic microorganisms. They produce antimicrobial peptides in their bodies and use them as a defense means against pathogenic microorganisms. Antimicrobial peptides are composed of 20-60 amino acids, and their molecular weights are about 2000-7000 D. Thus far, as many as about 200 antimicrobial peptides have been found from amphibians, insects, mammals, plants, microorganisms and fishes. The importance of peptides as physiologically active materials has been greatly recognized. These antimicrobial peptides are showing antimicrobial activity against a broad spectrum of microorganisms, including Gram-negative bacteria, Gram-positive bacteria, protozoa and fungi. Some of them are effective against both cancer cells and viruses. Most of the antimicrobial peptides kill target cells rapidly and specifically, and have unusually broad activity spectra.
By researching the primary structure and higher-order structure of the antimicrobial peptide, a lot of researcher find that when the antimicrobial peptide is in the hydrophobic environment of mimic membrane, its antimicrobial activity is related with the α-helix proportion. Another research result indicates that antimicrobial peptide kills the microorganisms by destructing the intact membrane of the microorganisms, which makes the membrane of the microorganisms leakage (Nakajima Y. et al., J. Biol. Chem, 262:1665-1669; Zasloff M. Nature, 2002, 415:389-395). So someone tries to search the antimicrobial peptides having stronger antimicrobial activity by increasing α-helix structure or heightening the positive charge amino acids proportion in the antimicrobial peptides (Broth W. B. et al., Antimicrobial Agents Chemotherapy, 2001, 45:1894-1895; Hong S. Y. et al., Peptides, 2001, 22:1669-1674).